1. Field of the Invention
The present invention relates to variable displacement compressors, and more particularly, to a variable displacement compressor for an air conditioner that alters its displacement according to the cooling load.
2. Description of the Related Art
Variable displacement compressors mounted on vehicles generally alter their displacement according to the temperature inside the vehicle to maintain the temperature of the vehicle interior at an appropriate value. Such a compressor is described in another of the applicants' patent applications filed with the United States Patent and Trademark Office (U.S. patent application Ser. No. 08/255,043) and the European Patent Office, which is published in European Patent Publication No. EP 0628722 A1. This prior art compressor has a housing with cylinder bores. A single-headed piston is reciprocally movable in each bore. A rotary shaft in the housing supports a swash plate, which is tiltable between a minimum inclined angle and a maximum inclined angle.
The displacement of the compressor corresponds with the inclined angle of the swash plate. When the swash plate is tilted at its maximum angle, the displacement of the compressor reaches its maximum. When the swash plate is tilted at its minimum angle, the compressor restricts discharge of compressed gas from the compressor. The inclined angle of the swash plate is adjusted by a pressure difference between the pressure in a crank chamber, which accommodates the swash plate, and the suction pressure. The pressure inside the crank chamber is thus altered to adjust the displacement of the compressor. To increase the pressure in the crank chamber, the pressure of a discharge pressure area, where compressed gas is discharged, is conveyed into the crank chamber through a pressurizing passage. To decrease the pressure in the crank chamber, the pressure of the crank chamber is released into a suction pressure area, where gas is drawn in, through a pressure releasing passage.
The compressor has a suction passage that introduces refrigerant gas from an external refrigerating circuit into the suction pressure area. A spool, which moves between a closing position and an opening position in correspondence with the inclined angle of the swash plate, is provided in the suction passage. When the swash plate is inclined at its minimum angle, the spool is moved to the closing position. This blocks the flow of refrigerant gas and prevents the gas from being drawn in. In this state, refrigerant gas circulates between the discharge pressure area, the crank chamber, and the suction pressure area through the pressurizing and pressure release passages and lubricates the interior of the compressor with oil mist suspended in the gas.
Loads in the axial and radial directions act on the rotary shaft. To cope with these loads, an angular contact bearing, which carries both axial and radial loads, is typically provided between the spool and the rotary shaft. In other words, a single bearing is employed to carry both axial and radial loads. This structure enables a reduction in the number of components and thus simplifies assembly.
However, it is required that the angular contact bearing have sufficient strength to carry the load acting in two directions on the rotary shaft. Thus, the size of the angular contact bearing is large. This results in a larger compressor.
Furthermore, it is preferable for the radial load of the rotary shaft to be supported at a position near the end of the shaft. However, since the angular contact bearing is located between the swash plate and the spool, the bearing is at a position separated from the end of the shaft. Accordingly, it is difficult to stably support the rotary shaft in the radial direction with the prior art structure. This may result in generation of vibration and noise during operation and cause a degradation in its performance.
In addition, refrigerant gas circulating between the crank chamber and the suction pressure area passes through the space between the swash plate and the spool in the above compressor. However, since the space defined between the swash plate and the spool is small, smooth circulation of the gas is impeded. This may cause insufficient lubrication of the angular bearing together with the other bearings. Insufficient lubrication will cause vibration and noise and reduce the life of the compressor.